A somewhat related question for Gary.
This question considers the differences in heat-shielding for LEO
spacecraft and lunar-return spacecraft, Gary.
I'm no expert on heat-shields, Gary, but since reentry from LEO involves roughly "half" the kinetic/heat energy of a lunar-return mission [assuming the LEO and lunar-return spacecraft are, roughly, the same weight].
MY QUESTION IS?... Is it a good rule-of-thumb to DOUBLE the mass of the ablative heatshield material on a LEO spacecraft [Command- Module] modified for a circumlunar mission ?